The phenomena exhibited by the radio-active bodies are extremely complicated, and some form of theory is essential in order to connect in an intelligible manner the mass of experimental facts that have now been accumulated. I have found the theory that the atoms of the radio-active bodies are undergoing spontaneous disintegration extremely serviceable, not only in correlating the known phenomena, but also in suggesting new lines of research.
The interpretation of the results has, to a large extent, been based on the disintegration theory, and the logical deductions to be drawn from the application of the theory to radio-active phenomena have also been considered.
The rapid advance of our knowledge of radio-activity has been dependent on the information already gained by research into the electric properties of gases. The action possessed by the radiations from radio-active bodies of producing charged carriers or ions in the gas, has formed the basis of an accurate quantitative method of examination of the properties of the radiations and of radio-active processes, and also allows us to determine with considerable certainty the order of magnitude of the different quantities involved.
For these reasons, it has been thought advisable to give a brief account of the electric properties of gases, to the extent that is necessary for the interpretation of the results of measurements in radio-activity by the electric method. The chapter on the ionization theory of gases was written before the publication of J. J. Thomson’s recent book on “Conduction of Electricity through Gases,” in which the whole subject is treated in a complete and connected manner.
A short chapter has been added, in which an account is given of the methods of measurement which, in the experience of the writer and others, are most suitable for accurate work in radio-activity. It is hoped that such an account may be of some service to those who may wish to obtain a practical acquaintance with the methods employed in radio-active measurements.
My thanks are due to Mr W. C. Dampier Whetham, F.R.S., one of the editors of the Cambridge Physical Series, for many valuable suggestions, and for the great care and trouble he has taken in revising the proof sheets. I am also much indebted to my wife and Miss H. Brooks for their kind assistance in correcting the proofs, and to Mr R. K. McClung for revising the index.
E. R.
Macdonald Physics Building,
Montreal,
February, 1904.